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BackgroundCOVID-19 antibody testing allows population studies to classify participants by previous SARS-CoV-2 infection status. Home lateral flow immune-antibody testing devices offer a very convenient way of doing this, but relatively little is known about how measurement and antibody variability will affect consistency in results over time. We examined consistency by looking at the outcome of two tests three months apart while COVID-19 infection rates were low (summer 2020 in the UK). MethodsThe KCL-Coronavirus Health and Experiences in Colleagues at Kings is an occupational cohort of staff and postgraduate research students. Lateral flow immune-antibody testing kits were sent to participants homes in late June 2020 and late September 2020. Participants also completed regular surveys that included asking about COVID-19 symptoms and whether they thought they had been infected. ResultsWe studied 1489 participants returned valid results in both June and September (59% of those sent kits). Lateral flow immune-antibody test was positive for 7.2% in June and 5.9% in September, with 3.9% positive in both. Being more symptomatic or suspecting infection increased the probability of ever being positive. Of those positive in June, 46% (49/107) were negative in September (seroreversion), and this was similar regardless of symptom characteristics, suspicion, and timing of possible infection. A possible outlier was those aged over 55 years, where only 3 of 13 (23%) had seroreversion. DiscussionThese results do not follow the pattern reported from studies specifically designed to monitor seropositivity, which have found greater consistency over time and the influence of presence, timing and severity of symptoms on seroreversion. We suggest several factors that may have contributed to this difference: our low bar in defining initial seropositivity (single test); a non-quantitative test known to have relatively low sensitivity; participants carrying out testing. We would encourage other studies to use these real-world performance characteristics alongside those from laboratory studies to plan and analyse any antibody testing.
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ObjectiveTo assess the feasibility of home antibody testing as part of large-scale study, the Kings College London Coronavirus Health and Experiences of Colleagues at Kings (KCL CHECK). MethodsParticipants of the KCL CHECK study were sent a SureScreen Diagnostics COVID-19 IgG/IgM Rapid Test Cassette to complete at home in June 2020 (phase 1) and September 2020 (phase 2). Participants were asked to upload a test result image to a study website. Test result images and sociodemographic information were analysed by the research team. ResultsA total of n=2716 participants enrolled in the KCL CHECK study, with n=2003 (73.7%) and n=1825 (69.3%) consenting and responding to phase 1 and 2. Of these, n=1882 (93.9%; phase 1) and n=1675 (91.8%; phase 2) returned a valid result. n=123 (6.5%; phase 1) and n=91 (5.4%; phase 2) tested positive for SARS-CoV-2 antibodies. A total of n=1488 participants provided a result in both phases, with n=57 (3.8%) testing positive for SARS- CoV-2 antibodies across both phases, suggesting a reduction in the number of positive antibody results over time. Initial comparisons showed variation by age group, gender and clinical role. ConclusionsOur study highlights the feasibility of rapid, repeated and low-cost SARS-CoV-2 serological testing without the need for face-to-face contact. What is already known about this subject?Higher education institutions have a duty of care to minimise the spread and transmission of COVID-19 in its campuses, and among staff and students. The reopening of higher education buildings and campuses has brought about a mass movement of students, academics and support staff from across the UK. Serological antibody studies can assist by highlighting groups of people and behaviours associated with high risk of COVID-19. What are the new findings?We report a framework for SARS-CoV-2 serological antibody testing in an occupational group of postgraduate research students and current members of staff at Kings College London. Over two phases of data collection, 6.5% (phase 1) and 5.4% (phase 2) tested positive for SARS-CoV-2 antibodies, with only 3.8% testing positive for antibodies in both phases, suggesting a reduction in positive antibody results over time. How might this impact on policy or clinical practice in the foreseeable future?Our study highlights the feasibility of rapidly deploying low-cost and repeatable SARS-CoV-2 serological testing, without the need for face-to-face contact, to support the higher education system of the UK.
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Background Definitive diagnosis of COVID-19 requires resources frequently restricted to the severely ill. Cohort studies must rely on surrogate indicators to define cases of COVID-19 in the community. We describe the prevalence and overlap of potential indicators including self-reported symptoms, suspicion, and routine test results, plus home antibody testing. Methods An occupational cohort of 2807 staff and postgraduate students at a large London university. Repeated surveys covering March to June 2020. Antibody test results from 'lateral flow' IgG/IgM cassettes in June 2020. Results 1882 participants had valid antibody test results, and 124 (7%) were positive. Core symptoms of COVID-19 were common (770 participants positive, 41%), although fewer met criteria on a symptom algorithm (n=297, 16%). Suspicion of COVID-19 (n=509, 27%) was much higher than positive external tests (n=39, 2%). Positive antibody tests were rare in people who had no suspicion (n=4, 1%) or no core symptoms (n=10, 2%). In those who reported external antibody tests, 15% were positive on the study antibody test, compared with 24% on earlier external antibody tests. Discussion Our results demonstrate the agreement between different COVID indicators. Antibody testing using lateral flow devices at home can detect asymptomatic cases and provide greater certainty to self-report; but due to weak and waning antibody responses to mild infection, may under-ascertain. Multiple indicators used in combination can provide a more complete story than one used alone. Cohort studies need to consider how they deal with different, sometimes conflicting, indicators of COVID-19 illness to understand its long-term outcomes.
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We report test results for SARS-CoV-2 antibodies in an occupational group of postgraduate research students and current members of staff at Kings College London. Between June and July 2020, antibody testing kits were sent to n=2296 participants; n=2004 (86.3%) responded, of whom n=1882 (93.9%) returned valid test results. Of those that returned valid results, n=124 (6.6%) tested positive for SARS-CoV-2 antibodies, with initial comparisons showing variation by age group and clinical exposure.
